This book is a collaborative effort of the following four persons (in alphabetical order):

• Sébastien Decugis is the original author and maintainer of the freeDiameter implementation. He was involved in IETF activities related to Diameter from 2008 to 2010, and he met Hannes and Jouni working on Diameter at IETF. His work was supported by the National Institute of Information and Communications Technology (NICT) and the WIDE Project, a cross‐company and cross‐university research project in Japan. Sébastien is not working for those structures anymore, but maintaining and developing the freeDiameter implementation on his free time, while NICT and WIDE are kindly maintaining the server resources required by the project.
• Jouni Korhonen, PhD, is a Principal R&D Engineer with Nordic Semiconductor. Previously he was with Broadcom and was active in Ethernet‐based base station architectures, Ethernet‐based fronthaul networks, and time‐sensitive networking. Prior to Broadcom Dr. Korhonen was with Nokia Siemens Networks and TeliaSonera where he was heavily involved in IPv6, DNS, mobility, and Diameter‐based core network signaling matters in 3GPP and IETF. He has also held multiple leadership positions within IETF and IEEE during his career, including chairing both the Diameter Maintenance and Extensions (DIME) and RADEXT WGs. Dr. Korhonen is still an active contributor with 38 published Requests for Comments (RFCs) to date. His current focus is on cellular Internet of Things and 3GPP system architecture evolution.
• Jean Mahoney had wanted to work on an oceanographic research vessel ever since she was a child. Having achieved her life goal right out of college, she discovered that she did not like being in the middle of the ocean. Thus she started on her career in computer networking and technical communication, explaining complex software systems to other developers, system administrators, and users. Jean has more than a decade's worth of experience with IETF specifications and the servers and clients built on top of them. Jean is currently the co‐chair of the IETF SIPCORE working group and Gen‐ART Secretary.
• Hannes Tschofenig co‐chaired the IETF DIME working group from March 2006 till March 2010, when he was elected to the Internet Architecture Board (IAB) of the IETF. He is co‐author of over 80 RFCs, including several Diameter specifications. His work on Diameter in the IETF was sponsored by Siemens (from 2001 to 2007) and later by Nokia Siemens Networks (from 2007 to 2013), i.e., telecommunication equipment manufacturers selling Diameter‐based products. Hannes is now employed by Arm Ltd., where his focus is on improving the security of Internet of Things devices.